Currently there is a mismatch between the email addresses
that are accepted by the Devise email regular expression and
what is an actual valid email address according to RFC 3696 and
what will therefore be sent reliably by most SMTP servers.

This commit replaces the use of Devise's default regex with
the valid_email gem which is stricter.

Related Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/215919